I studied comets, and published some original research on comet tail interaction with the solar wind, not that my opinion matters much, but in my experience for what most researchers classify comets, this is absolutely a megacomet. It's more than twice as large as the one I kept in my mind from a decade ago that I considered one of the larger comets and Humason [0] was only about 40km in diameter.

Yes, cold bodies that have the properties of a comet may have lived the life of a comet at some point, or will again in the future, but currently something that shares a common center of mass with another object in a pretty stable orbit is not really going to get the full comet red carpet at the comet awards :)

[0] https://en.wikipedia.org/wiki/Comet_Humason